Field of the Invention
The present invention relates generally to a driveline system for a vehicle and, more particularly, to a final drive (chain or belt) adjusting system on a single track vehicle (e.g., motorcycle) or multi track vehicle having a trailing arm suspension. Yet more specifically, the present invention relates to a system and apparatus for providing both static and dynamic adjustment of the tension in an endless loop final drive.
Description of the Prior Art
Dynamic Chain Adjustment and Causes of Variations in Chain Tension:
Vehicles, such as motorcycles, often use a chain drive to deliver power from the motor or engine to one or more ground-engaging wheels. In the disclosure which follows, the term “chain drive” refers to the class of endless loop drive systems which may comprise a roller chain, silent chain, synchronous and non synchronous belt drive, or any other type drive in this class. Further, sprockets, pulleys, sheaves or the like may be referred to as “pinions.” Chain drives are often used on vehicles such as motorcycles which employ a rear wheel connected to the vehicle main frame by means of a pivoting, trailing, swing arm.
In many chain driven vehicles, and in other instances where chain drives are used, a chain tensioner is employed to maintain tension in the final drive chain so that the chain is properly engaged with the chain sprockets, or pinions, on an output shaft and a rear wheel. These known chain tensioners, typically rollers, typically are biased toward the drive chain with a spring or other compliant biasing member. The force of the biasing member is such that, as the rear wheel bounces up and down with respect to the vehicle frame and output shaft (or driving pinion), the chain tensioner moves up and down by a spring force or torque to remain in contact with the drive chain, thereby preventing the chain from slipping on the pinions (or sprockets). Other types of tensioners include chain rubs that are fixably mounted to a motorcycle frame, such that a drive chain slides against the chain rub to thereby remove some of the slack that exists in the drive chain. These chain tensioners which account for the chain slack during suspension motion can be considered as “dynamic” chain tensioners.
Static Chain Adjustment:
In addition to a “dynamic” chain tensioner, there are known in the art “static” chain tension adjusters. Static adjusters are used to account for wear of the pinions and/or the chain, and also to accommodate manufacturing tolerances on the vehicle. Static adjustment typically is performed manually at regular maintenance intervals (depending on vehicle usage). One method for static adjustment of the chain is by moving the driven wheel relative to the trailing arm. To perform this type of static adjustment the vehicle must be stopped. The wheel axle must be loosened and the axle moved, typically with threaded adjusters on each side of the wheel. The wheel must be aligned so that the pinions are in the same plane, and the wheel axle must then be re-tightened. Problems arise if the wheel is not aligned properly; the chain may heat up and wear quickly, and/or the vehicle may exhibit poor handling qualities due to wheel misalignment. It also is possible to tighten the chain incorrectly, in such a fashion that the adjustment appears correct, but when the suspension is worked the chain becomes overloaded or overloads the vehicle's pinion shafts and bearings.
In addition to moving the driven wheel for static chain adjustment, another known method of static adjustment is to move the trailing arm pivot relative to the chassis. A static adjustment is carried out similarly to the fashion described above, except that the trailing arm pivot is loosened. In either of these methods, the adjustment process can be time consuming and messy.
Chain Drive Design Limitations:
Because of the dynamic chain tension variation due to suspension motion, typical chain drive designs locate the driving pinion as close as possible to the trailing arm pivot axis. In some designs, such as seen in U.S. Pat. No. 4,003,443, the driving pinion is located co-axially with the trailing arm pivot axis to eliminate chain tension variation. Although this reduces chain slack variation of the chain drive, it greatly limits the ability to improve vehicle dynamics by utilizing different drive chain geometries.
Engine Braking and Reverse Drive Problems:
Spring loaded chain tensioners also have problems with heavy engine braking or reverse drive of the chain drive system. It is well known that a chain drive or belt drive loop has a loaded portion and an unloaded portion, the loaded portion being the length of chain or belt that is in high tension as it pulls on a driven pinion or sprocket to impart rotary motion to a wheel. Typically, a spring loaded tensioner is on the unloaded loose or return side of the chain drive. Under reverse loading, the chain tension switches “sides,” and the previously unloaded loose side becomes tight while the formerly loaded portion, the tight side, becomes loose. Under these circumstances, the spring on the tensioner cannot supply a sufficiently large tension force to counterbalance the reverse chain load, and the chain can become very loose and skip or come off the pinions. If the spring tension is increased to compensate for the change in tension due to reverse loading, than the high tension tends quickly to wear the chain drive. Yet another method is to employ an additional spring loaded chain tensioner on the typical tension side of the chain drive. Then, when the chain undergoes a reverse load, this additional chain tensioner adjusts the now loose side of the chain. Such additional spring loaded tensioners add cost and complexity to vehicle configuration. Further, the chain drive tends to exhibit undesirable “slack deadband,” in which the driven pinion can rotate back and forth tightening and loosening the different sides of the chain drive relative to the driven pinion.
Previous efforts to statically or dynamically adjust chain tension are disclosed in U.S. Pat. No. 4,705,494 to Gibson; U.S. Pat. No. 4,299,582 to Leitner; U.S. Patent App. Pub. No. 2009/0241742 to Gilgallon et al.; U.S. Pat. No. 4,034,821 to Stoddard et al.; U.S. Pat. No. 3,834,246 to McGilp; and U.S. Pat. No. 4,433,747 to Offenstadt. While the teachings of these patent publications are incorporated herein by reference, any discussion of the prior art throughout this disclosure should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
In sum, there are several main problems with prior art chain adjusting systems, including:                1. Static driveline adjustment requires movement of critical vehicle components, which must be properly aligned for driveline functioning and vehicle functioning;        2. Static driveline adjustment requires loosening of critical vehicle components which must be done with the vehicle stopped and usually on a stand;        3. Static adjustment is labor intensive and inconvenient;        4. Improper chain adjustment can damage driveline components such as the chain, the pinions or the pinion shaft bearings;        5. Final drive geometry is designed around limiting variations in chain path length during suspension travel, instead of improved vehicle dynamics;        6. Final drive dynamic compensation systems tend only to work in one direction of chain tension (forward drive);        7. A spring loaded tensioner would require high spring load to tension the chain during engine braking, or reverse drive; this added tension would reduce the efficiency and life of the drive chain.There is an unmet need for an improved final drive tensioning system which ameliorates or eliminates these problems. Against the foregoing background, the following invention was developed.        